Microwave strip transmission line circulators



L. DAVIS, JR

Nov. 6, 1962 I MICROWAVE STRIP TRANSMISSION LINE CIRCULATOR Filed Feb. 29, 1960 20 //v|/EA/7'0/? LUTHER DAV/.5; JR.

TTOR/VEY stances.

United States Patent Qfifice Brim Patented Nov. 6, 1962 ware Filed Feb. 29, 1960, Ser. No. 11,740 Claims. (Cl. 333-11) This invention pertains generally to microwave circulators, and more particularly to improved ferrimagnetic microwave circulators employing strip transmission line configuration. As employed herein, the term ferrimagnetic is intended to connote materials having negligible electrical conductivity and exhibiting either ferrimagnetic or ferromagnetic effects.

Ferrimagnetic materials find wide use in microwave devices as the art advances. Exemplary of devices employing magnetized ferrimagnetic materials are gyrators, isolators, directional phase shifters and circulators. Circulators are considerably more complicated circuit elements than, for example, isolators, and the uses proposed for them are typically more sophisticated than those for isolators. An important distinction between circulators and isolators is that the former diverts or otherwise makes use of input power, rather than destroying it, as does the latter. It is a basic characteristic of microwave circulators that energy introduced into a first port will be presented (ignoring losses) as an output solely at a second port (for a given set of operating parameters), energy at such second port appears at only a third port, and so on, with substantial isolation being provided between a selected input port and all other ports except the particular output port. The term circulator thus connotes a commutation of power from one transmission terminal to another.

It is well known that a magnetized ferrirnagnetic body is an anisotropic medium, and that a microwave device including such a body may be electromagnetically asym metrical even though it has geometrical symmetry. It is this asymmetry of electromagnetic characteristics that renders ferrimagnetic devices the interesting and useful tools that they are, and different theories (based upon field displacement and perturbation theory, for example) have been advanced as to the basis for such asymmetric characteristics.

The anisotropic electromagnetic properties of magnetized ferrimagnetic bodies have been utilized by prior workers in the art to provide Y-junction and other circulators of hollow waveguide configuration, and these prior art devices have proven satisfactory for some applications. However, these prior art circulators have lacked sufficient electrical bandwidth in many applications. In addition, the size and width of the devices of the prior art are often greater than can be tolerated in many in- Further, the adequate dissipation of heat from the ferrimagnetic members of prior circulators has been difficult.

It is accordingly a primary object of the present invention to provide a microwave circultaor of relatively small and lightweight construction.

An additional object of the present invention is to provide a microwave circulator being characterized by an increased electrical bandwidth.

Another object of the present invention is to provide a microwave circulator having improved heat-dissipation characteristics.

In accordance with the present invention, the above and other objects are achieved by means of a microwave circulator device employing strip transmission line configuration, as opposed to hollow waveguide members. In the exemplary embodiment described herein, the circulater body includes a pair of parallel ground plane members held in spaced-apart relationship by a peripheral cover member. Three coaxial connectors are disposed about the peripheral cover in symmetrical relationship, with the center conductor of each of the connectors being connected to the outer end of a respective one of the three arms of a conductive spider member which is positioned midway between and parallel with the ground plane members to provide a strip transmission line configuration of three branches.

In order to obtain circulator action, a pair of ferrimagnetic members are positioned substantially centrally within the circulator, one on either side of the central portion of the spider member, and a magnetic field of fixed intensity is established within the ferrite member in a direction perpendicular to the spider and ground plane members. As will be understood by those skilled in the art, this steady-state magnetic field is of an intensity amplitude which is significantly removed from (being either greater or smaller) that connected with ferrimagnetic resonance at a given microwave frequency and for a given geometry. The three coaxial connectors constitute the ports of the circulator, and a signal applied to a first of these ports effectively appears at only a second port, with signals applied to the second port appearing only at the third, and so on, for a given field polarity of magnetic energization. With the D.-C. magnetic field .reversed, the sense of the commutation between ports is reversed.

With the above considerations and objects in mind the invention itself will now be described in connection with a preferred embodiment thereof given by way of example and not of limitation, and with reference to the accompanying drawings, in which:

FIG. 1 is a plan view of the microwave circulator of the present invention, with the D.-C. magnetic field means being removed for the sake of clarity.

FIG. 2 is a sectional view taken on line 22 in FIG. 1.

FIG. 3 is a fragmentary elevation view of a modification of the device shown in FIGS. 1 and 2.

In the exemplary embodiment shown in FIGS. 1 and 2, a pair of circular ground plane members 10 and 12 are shown mounted in parallel spaced-apart relationship by means of a peripheral cover member 14, with the plates 10 and 12 and the cylindrical member 14 together forming the body of the circulator. These three members are of electrically conductive material, and may conveniently be secured together by a plurality of threaded fasteners 16 disposed about the peripheries of the two plates'ltl and 12. A plurality of coaxial connectors 18, 2t} and 22 are symmetrically disposed about the cover member 14 to form the ports of the circulator. The center conductors 24, 26 and 28 of the three coaxial connectors are connected to the ends of respective arms of a conductive spider member 30, such spider member having a central portion 32 in substantial registry with the central portions of the ground plane members 10 and 12..

As will be evident to those skilled in the art, energy in coaxial lines connected to the connectors 18, 2t) and 22 will be propagated into the circulator of the present invention by means of the strip transmission line confiuration of the components therein, and, similarly, microwave energy within the circulator will be propagated by such strip transmission line configuration to one or more of the ports formed by the connectors 18, 2t) and 22, for transmission through coaxial lines connected thereto.

In order to render this three port strip transmission line junction a circulator, a pair of ferrimagnetic bodies 34 and 36 are suitably mounted (by means not shown) on opposite sides of the conductive spider member 3%, and in substantial registry with the central portion 32 thereof. The particular composition of the members 34 and 36 is not a necessary element of the present invention, and any substantially electrically nonconductive materials exhibiting ferrimagnetic or ferromagnetic effects may be employed. Yttrium iron garnet polycrystalline materials are exemplary for this purpose.

In the operation of the device depicted in FIGS. 1 and 2, a steady-state or D.-C. magnetic field is applied to the ferrite bodies 34 and 36 in one sense or the other in a direction substantially perpendicular to the plane of the spider member 30, such applied magnetic field being schematically indicated by the dot-dash lines 38 in FIG. 2, and being of a magnitude which is removed from (being either significantly greater or smaller) that connected with ferrimagnetic resonance at the applied microwave frequency and for the given geometry. With the D.-C. magnetic field passing through ferrimagnetic bodies 34 and 36 in a selected direction (e.g., into the drawing page of FIG. 1), microwave energy introduced into the circulator at the port formed by coaxial connector 18 will appear as an output (neglecting losses) at the port formed by connector 20, with no effective output appearing at connector 22. With the D.-C. magnetic field maintained in this same direction, a singal applied to connector 20 will appear as an output signal at connector 22 with no effective coupling toward connector 18. Similarly, with the D.-C. magnetic field maintained in this first polarity, an input signal at connector 22 will produce an output at only connector 18. Thus, a commutation of signals in a given direction between the several ports of the circulator is achieved. Where the polarity or sense of the applied D.-C. magnetic field is reversed from that first assumed herein, the direction of commutation between ports is also reversed, and an input at connector 18 appears as an output at connector 22, et cetera.

FIG. 3 shows a modification of the device of FIGS. 1 and 2, with corresponding elements bearing like reference numerals. Thus, the ground plane members and 12 are supported in parallel spaced-apart relationship by means of the cylindrical cover member 14, the latter having a plurality of coaxial connectors (one of which is indicated at 20) mounted thereon. The conductive spider member 30 is mounted within the circulator body substantially midway between and parallel with the ground plane members 10 and 12, with the outer ends of the spider arms being connected to the center conductors (one of which is indicated at 26 in FIG. 3) of respective ones of the coaxial connectors mounted on cover member 14.

A pair of ferrimagnetic members 40 and 42 are mounted on opposite sides of the spider memebr 30, and in substantial registry with the central portion 32 thereof, as well as with the central portions of ground plane members 10 and 12. In contrast to the ferrimagnetic members 34 and 36 shown in the preceding figures of the drawing, members 40 and 42 are of sufiicient thickness to result in a closely contiguous relationship between the upper and lower faces thereof, respectively, and the opposing areas of the inner faces of ground plane members 10 and 12. The intimate contact between the upper face of member 40 and the contiguous face of ground plane member 10 results in an efficient heat transfer between the ferrite 40 and the member 10. Similarly, efiicient heat transfer takes place between the lower face of member 42 and the upper face of member 12. As is common with microwave devices employing ferrimagnetic members, considerable quantities of heat may be generated within the members 49 and 42, and the good thermal contact between these members and the respective ground plane members provides a ready sink for such heat. To improve the efficiency with which such heat may be dissipated, cooling chambers 44 and 46 are provided in intimate contact with the outer faces of members 10 and 12, and a suitable coolant is circulated through such chambers by means not shown.

It will be understood that the operation of the device shown in FIG. 3 is substantially the same as that described in connection with FIGS. 1 and 2, with the D.-C. magnetic field being applied to ferrimagnetic members 40 and 42 by a suitable magnet the pole pieces 48 and 50 of which are shown in FIG. 3. Where circulator action or commutation is desired in but one direction, the pole pieces 48 and 50 may form a part of a permanent magnet of appropriate polarity. On the other hand, where it is desired to reverse the sense of the circulator operation, it is necessary to reverse the sense of the applied D.-C. magnetic field. Suitable means for achieving such field reversal are indicated schematically in FIG. 3 by the solenoid '52 which is energized by a D.-C. source 54 through a reversing switch 56. Upon reversal of switch 56 from one position to another, the magnetic field passing through members 40 and 42 is reversed in polarity, and the circulator action is correspondingly reversed.

The invention has been described above in some detail, and with particular reference to the application of strip transmission line configuration to a three port Y-junction circulator. However, it will be evident to those skilled in the art that the invention is equally applicable to circulators having other than three ports therein. In addition, the circulator ports may take the form of hollow waveguide connectors with central coupling loops being connected to the outer ends of the arms of the strip transmission line spider member. Further, it will be understood that the strip transmission line structure of the present invention need not necessarily be in the form of a central conductor between two spaced-apart ground planes. Instead, the device of the invention may equally well comprise the spider member disclosed herein and only one ground plane member. In such configuration, the spider and the ground plane member would be mounted in parallel spaced-apart relationship with a ferrimagnetic member therebetween, with a source of D.-C. magnetic field, and a plurality of appropriate connectors suitably matched to the strip transmission line structure so formed. Thus, the invention is not to be considered as limited to the particular details given, nor to the specific application to which reference has been made during the description of the device, except insofar as may be re' quired by the scope of the appended claims.

What is claimed is:

1. A circulator comprising a plurality of strip transmis sion lines coupled together at a common point, said transmission lines being oriented with their axes defining equal angles, each line including a center conductor disposed between two outer conductors, means electrically connecting together the center conductors of each of said transmission lines at said common point, at least one body of ferrite material disposed at said common point between said center conductor and one of said outer conductors, at least one other body of ferrite material dis posed at said common point between said center conductor and said other outer conductor, and means magnetizing said ferrite bodies in a direction substantially parallel to the electric field of waves conducted by said lines and with a strength such that electric waves conducted by each of said lines couple to only one other of said lines and said last-mentioned coupling is nonreciprocal.

2. A circulator as in claim 1 and in which said outer conductors of each of said transmission lines extend substantially beyond the edge of the associated center conductor.

3. A circulator as in claim 1 and in which each of said strip transmission lines couples to a separate connector at the same distance from said common point.

4. A circulator as in claim 1 and in which each of said bodies of ferrite material has at least one dimension parallel to a common plane which is greater than at least one dimension of said center conductors parallel to said common plane.

References Cited in the file of this patent UNITED STATES PATENTS 2,946,966 Crowe July 26, 1960 10 2,978,649 Weiss Apr. 4, 1961 3,015,787 Allin et a1. Jan. 2, 1962 6 OTHER REFERENCES Electrical Manufacturing, February 1959, pages Aulbl: IRE Transactions on Microwave Theory and 5 Techniques, April 1959, pages 238-246.

Swanson et al.: 1958 IRE Wescon Convention RecordPart 1, pages 151-156.

Chait et al.: NRL Progress Report, March 1958 (made available to public through OTS on Apr. 11, 1958), page 50.

Seidel: Journal of Applied Physics, February 1957, pages 218-226. 

1. A CIRCULATOR COMPRISING A PLURALITY OF STRIP TRANSMISSION LINES COUPLED TOGETHER AT A COMMON POINT, SAID TRANSMISSION LINES BEING ORIENTED WITH THEIR AXES DEFINING EQUAL ANGLES, EACH LINE INCLUDING A CENTER CONDUCTOR DISPOSED BETWEEN TWO OUTER CONDUCTORS, MEANS ELECTRICALLY CONNECTING TOGETHER THE CENTER CONDUCTORS OF EACH OF SAID TRANSMISSION LINES AT SAID COMMON POINT, AT LEAST ONE BODY OF FERRIT MATERIAL DISPOSED AT SAID COMMON POINT BETWEEN SAID CENTER CONDUCTOR AND ONE OF SAID OUTER CONDUCTORS, AT LEAST ONE OTHER BODY OF FERRITE MATERIAL DISPOSED AT SAID COMMON POINT BETWEEN SAID CENTER CONDUCTOR AND SAID OTHER OUTER CONDUCTOR, AND MEANS MAGNETIZING SAID FERRITE BODIES IN A DIRECTION SUBSTANTIALLY PARALLEL TO THE ELECTRIC FIELD OF WAVES CONDUCTED BY SAID LINES AND WITH A STRENGTH SUCH THAT ELECTRIC WAVES CONDUCTED BY EACH OF SAID LINES COUPLE TO ONLY ONE OTHER OF SAID LINES AND SAID LAST-MENTIONED COUPLING IS NONRECIPROCAL. 